This invention relates to plastic article shaping or the like and specifically to the rotational control of a tire building drum or mandrel and apparatus associated therewith.
The building of a tire is a manual operation during the time when the various tire components are being placed upon the building drum or mandrel. The usual operation is carried out by the operator withdrawing stock from a servicer machine or source of supply and placing same upon the tire building drum or mandrel. The amount of stock withdrawn from the source of supply must be sufficient to encompass said mandrel and the stock already thereon. Thus, the mandrel or tire building drum may be rotated for one revolution or less and this operation is carried out by the operator moving a foot switch to control drum rotation and, thus, control the "run on" of the stock with respect to the mandrel or building drum.
In supplying stock to a building drum or mandrel, the operator will frequently actuate the foot switch to start and stop the motor and thereby assure that the plystock will not be wrapped around the building drum or mandrel for more than one revolution. The constant interruption of the building drum rotation will result in the plystock being continuously and repeatedly tensioned and relaxed, which produces undue stresses in the plystock material resulting in non-uniform cord end distribution. This is particularly true with radial ply body cord materials wherein the cord ends run parallel to the axis of the building drum and which ends are thus easily dispositioned. Thus, it becomes highly desirous to have an apparatus that would eliminate the frequent stops and starts of the rotating building drum during delivery of the plystock thereto.
A stock carrying rotational drum having associated therewith a device to limit the movement of the drum to a single or one complete revolution are known to those skilled in the art. Such devices are referred to as one revolution devices and same are usually chain driven from the main drum shaft by a suitable chain and sprocket assembly on a one-to-one ratio. In such devices, the driven shaft member carries cam elements that rotate with the driven shaft at all times during rotation of the drum member. There are also shaft and gear members that rotate when clutched in and there are arm members that carry limit switches which are pivoted into contact with said cam elements when energized by suitable solenoid actuation.
During a tire assembly operation, a tire building drum must rotate frequently and at different rotational speeds. A one revolution devices which is chain driven directly from the main drum shaft is provided with stop cams that are located and held on the driven shaft member by frictional pressure only, so that, they can be easily adjusted. Such an arrangement often results in said cams being dispositioned relative to their present drum location or relative to each other by the sudden stop - start actions of the tire building drum. In addition, the relative settings of the cams are known to change during high rotational drum speeds that are used when consolidating tire components. An apparatus or system of the foregoing type is not too reliable because of frequent readjustments that are necessary and the direct drive arrangement is usually costly to maintain. In view of the inaccuracies that can arise from the cam elements, a direct driven one revolution device can be of little value when constructing radial tires which require extremely accurate and consistent placement of all components on the tire building drum.